Photoinduced processes of newly synthesized bisferrocene- and bisfullerene-substituted tetrads with a triphenylamine central block

Article abstract of DOI:10.1016/j.jorganchem.2009.01.011

Photoinduced electron transfer processes of two newly synthesized tetrads with a triphenylamine (TPA) as central building block, to which bisfullerenes (C₆₀) and bisferrocenes (Fc) are covalently connected, have been studied. One of them has a TPA linked with one C₆₀ moiety and two ferrocene moieties C₆₀-TPA-(Fc)₂ and another tetrad has a TPA linked with two C₆₀ moieties and one ferrocene unit (C₆₀)₂-TPA-Fc. The photophysical properties of (C₆₀)_m-TPA-(Fc)_n have been investigated by applying the picosecond time-resolved fluorescence and nanosecond transient absorption techniques in both polar and nonpolar solvents. The charge separation process via the excited singlet state of the C₆₀ moiety of the C₆₀-TPA-(Fc)₂ is more efficient than that of the (C₆₀)₂-TPA-Fc. It is found that the ratio of Fc-donor to C₆₀-acceptor affects charge separation efficiency via the excited singlet state of the C₆₀ moiety.

Full text of DOI:10.1016/j.jorganchem.2009.01.011

Journal of Organometallic Chemistry 694 (2009) 1818–1825
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Photoinduced processes of newly synthesized bisferrocene-
and bisfullerene-substituted tetrads with a triphenylamine central block
a,
Jai Han Seok a, Seung Ho Park a, Mohamed E. El-Khouly b,c, Yasuyuki Araki b, Osamu Ito b, , Kwang-Yol Kay
*
*
a Department of Molecular Science and Technology, Ajou University, Wonchon-dong, Youngtong-gu, Suwon 443-749, South Korea
b Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Sendai 980-8577, Japan
c Department of Material and Life Science, Graduate School of Engineering, Osaka University, SORST, Japan Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Photoinduced electron transfer processes of two newly synthesized tetrads with a triphenylamine (TPA)
as central building block, to which bisfullerenes (C60) and bisferrocenes (Fc) are covalently connected,
have been studied. One of them has a TPA linked with one C60 moiety and two ferrocene moieties
C60–TPA–(Fc)2 and another tetrad has a TPA linked with two C60 moieties and one ferrocene unit
Received 14 November 2008
Received in revised form 31 December 2008
Accepted 8 January 2009
Available online 14 January 2009
(C60)2–TPA–Fc. The photophysical properties of (C60)m–TPA–(Fc)n have been investigated by applying
the picosecond time-resolved fluorescence and nanosecond transient absorption techniques in both polar
and nonpolar solvents. The charge separation process via the excited singlet state of the C60 moiety of the
C60–TPA–(Fc)2 is more efficient than that of the (C60)2–TPA–Fc. It is found that the ratio of Fc-donor to
C60-acceptor affects charge separation efficiency via the excited singlet state of the C60 moiety.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Fullerene
Electron transfer
Ferrocene
1. Introduction
In the present report, we synthesized two tetrads with a TPA
as a central block, to which fullerenes (C60) and ferrocenes (Fc)
The construction of artificial photosynthetic models to mimic
natural photosynthesis through the designing of covalently linked
electron-donor and electron-acceptor moieties is the object of
great interest. The interest lies in the development of efficient or-
ganic solar cells [1–4] and other areas of nanotechnology such as
photonics or sensors [5–8]. In this respect, C60 has been employed
as an excellent electron-acceptor [9,10], similar to quinones, and
its visible light absorption allows efficient photo-sensitizer induc-
ing such events as energy transfer (EN) and electron transfer (ET)
via the excited state of C60 moiety in fullerene-donor molecular
systems [11,12].
The donor ability determines the nature of the photophysical
events in these fullerene-donor systems; ferrocene (Fc) units allow
an efficient electron transfer event that generates the radical ion
pair [13–17]. Moreover, triphenylamine (TPA) derivatives also
have been recognized as good electron-donors with respect to
the photo-excited C60 [18,19].
are covalently connected. One tetrad has a TPA linked with one
C60 moiety and two Fc moieties, C60–TPA–(Fc)2 and another tet-
rad has a TPA linked with two C60 moieties and one ferrocene
unit, (C60)2–TPA–Fc as shown in Fig. 1. These new compounds
are thought to be dendrimer-like light-harvesting molecules,
which have received increased attentions in recent years [22–
25]. Some ferrocene-substituted fulleropyrrolidine derivatives
with multi-vinylene bridges have been reported to provide a
very efficient photoinduced energy transfer [26–28]. Thus, it is
interesting to compare the photophysical properties of these bis-
ferrocene- and bisfullerene-substituted molecules with a TPA
central block.
The photophysical properties of these compounds have been
studied by the time-resolved spectroscopic techniques and com-
pared with those of the single donor–acceptor triad (C60–TPA–Fc)
reference molecule. These molecular systems are expected to pres-
ent efficient photoinduced electron transfer (PET) processes to give
long-lived radical ion pairs.
In the strategic view points of synthesis, fullerenes such as C60
are attractive cores due to their easy chemical functionalizations,
which allow the incorporation of most functional groups [20]. Fur-
thermore, the TPA derivatives are also attractive building blocks to
connect the donor unit and acceptor unit, in addition to their elec-
tron-donor character [21].
2. Results and discussion
2.1. Synthesis and characterization
The two target tetrads C60–TPA–(Fc)2 2 and (C60)2–TPA–Fc 3 as
well as the reference triad C60–TPA–Fc 1 have been synthesized
according to the procedures depicted in Scheme 1.
* Corresponding authors. Fax: +82 31 213 3652.
E-mail addresses: ito@tagen.tohoku.ac.jp (O. Ito), kykay@ajou.ac.kr (K.-Y. Kay).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.01.011

J.H. Seok et al. / Journal of Organometallic Chemistry 694 (2009) 1818–1825
1819
H3C
N
Fe
Fe
Fe
N
CH3
N
N
CH3
N
CH3
N
N
Fe
C60−TPA−−Fc (1)
C60−TPA−(Fc)2 (2)
(C60)2−TPA−Fc (3)
Fig. 1. Molecular structures of compounds 1, 2 and 3.
Every step of the reaction sequence proceeded smoothly and
efficiently to give a good-or-moderate yield of the product (see
Section 4 for synthetic details).
Commercially available diphenylamine was coupled with 1-
bromo-4-iodobenzene by Buchwald–Hartwig method [29,30] to
give 4-bromotriphenylamine (4) in 57.5% and subsequently Vils-
meier formylation [31,32] was carried out to produce aldehyde 5
in 91.0%.
direct evidence for the structures of 1, 2 and 3, showing a peak
at m/z = 1233.1 [M+2]+ for 1, a peak at m/z = 1439.8 [MꢁH]+ for
2, and a peak at m/z = 1825.49 [MꢁFc]+ for 3, respectively. Further
confirmation of the hybrid (C60)n–TPA–(Fc)n structures was ob-
tained from UV–Vis spectra of 1, 2 and 3, which contain a dihydro-
fullerene absorption band at around 430 nm together with the
expected ferrocene and TPA-bands at around 330–360 nm.
Coupling of ferrocenylvinyl group to 5 was catalyzed by the
Heck reaction [33,34] using Pd2dba3 catalyst complex with dppf
to afford 6 in 65.0%, and finally, fulleropyrrolidine formation was
achieved by 1,3-dipolar cycloaddition reaction between aldehyde
6 and C60 in the presence of excess N-methylglycine (sarcosine) un-
der the condition described by Prato et al. [35] to give C60–TPA–Fc
(1) in 15.3%. C60–TPA–(Fc)2 tetrad (2) was also prepared in a very
similar way. However, in the synthetic course of (C60)2–TPA–Fc tet-
rad (3), direct double formylation of TPA by the Vilsmeier reaction
proved to be difficult due to the deactivation effect of the first car-
bonyl group on TPA, and mainly gave a monoformylated TPA under
normal stoichiometry of POCl3/DMF (up to 3.5 equiv.). With a large
excess of POCl3/DMF (ꢀ10 equiv.), the diformylated TPA 10 was
produced with a yield of 42.0%. Subsequent bromination of 10
was performed using bromine to give 11 in 87.0%, and then Heck
reaction between 11 and vinylferrocene was carried out using
Pd(OAc)2 as catalyst to afford 12 in 40.0%. Finally, fulleropyrroli-
dine formation was achieved by Prato’s method [35] to give the
(C60)2–TPA–Fc tetrad (3) in 50.0%. Although the tetrad 3 should
be obtained as a stereo-isomeric mixture due to the formation of
two asymmetric centres in twofold cycloaddition reaction, high
resolution 1H NMR spectrum (400 MHz) of tetrad 3 showed the
presence of only one stereoisomer. The same results for similar
derivatives were often observed by our group [21,36] (see also Sec-
tion 4).
2.2. Electrochemistry
The electrochemical properties of C60–TPA–(Fc)2, (C60)2–TPA–Fc
and C60–TPA–Fc were probed by cyclic voltammetry in DCB solvent
and n-Bu4NClO4 as a supporting electrolyte. As a general feature,
these compounds gave rise to three reversible one-electron reduc-
tion waves in the cathodic observation window; they were attrib-
C60
uted to three reduction potentials (Ered ) of the C60 cage; the first
C60
Ered
value was ꢁ0.82 V vs. Fc/Fc+ [21,36]. In the anodic region,
single reversible oxidation potential of Fc (EoxFc) was observed at
ꢁ0.07 V; additional reversible oxidation was observed at +0.80 V
for TPA (EoxTPA). The free energies (
DGCR) of the radical ion pairs
were calculated from the Rhem–Weller equation [38–40]. For
example, the
D
GCR value of C60Åꢁ–TPA–FCÅ+ was evaluated to be
ꢁ0.75 eV and the
D
GCR value of C60Åꢁ–TPAÅ+–-Fc was ꢁ1.62 eV in
DCB. From these
DGCR values and excited energies (E00) of C60
(=1.70 eV), the free energy changes of the charge separation pro-
cess (D
GCS) via the excited singlet state of C60 (1C6ꢂ0) were calcu-
lated to be ꢁ0.95 and ꢁ0.08 eV, respectively, in DCB. For other
C60–TPA–(Fc)2 and (C60)2–TPA–Fc, almost the same values were
evaluated. For TPAÅ+-C60Åꢁ, the
DGCR and DGCS values were calcu-
lated to be ꢁ1.62 and ꢁ0.08 eV, respectively.
2.3. Steady-state absorption studies
C60–TPA–Fc (1), C60–TPA–(Fc)2 (2) and (C60)2–TPA–Fc (3) are
very soluble in aromatic solvents (i.e., toluene (TN), o-dichloroben-
zene (DCB), benzonitrile (PhCN)) and other common organic sol-
vents (i.e., carbon disulfide, acetone, CH2Cl2, CHCl3, THF). The
structure and purity of the new compounds were confirmed by
1H NMR, 13C NMR and IR spectroscopies, MALDI-TOF mass spec-
troscopy, and elemental analysis.
The absorption spectra of C60–TPA–Fc are shown in Fig. 2. The
absorption spectrum of C60–TPA–Fc exhibits a sharp absorption
band at 430 nm and a weak one at 700 nm, which are attributed
to the C60 moiety, whereas the weak band of the Fc unit may be
hidden near the 400 nm band of the C60 moiety, and the TPA unit
shows the absorption band near 330 nm. Thus, the remaining
broad band in the whole visible region can also be attributed to
1H NMR spectra of 1, 2 and 3 in CDCl3 are consistent with the
proposed structures, showing the expected features with the cor-
rect integration ratios. The signals of pyrrolidine protons in 1, 2
and 3 appeared as two doublets (geminal protons), and a singlet
in the d = 4.60–4.92 ppm region, which is consistent with the spec-
tra obtained for similar derivatives [37]. Protons of the ferrocene
moiety showed typical three singlets in the d = 4.04–4.43 ppm re-
gion. 13C NMR spectra contained the signals corresponding to the
sp2 and sp3 atom of C60 and the expected signals corresponding
to the organic addends. The MALDI-TOF mass spectra provided a
the C60 moiety. Similar spectral features were observed for C60–
TPA–(Fc)2 and (C60)2–TPA–Fc, in which the latter shows twice in-
tense bands in the visible region.
2.4. Fluorescence studies
The fluorescence spectra of the reference C60 compounds show
the emission peaks at 710 nm as a mirror image of the 700 nm
absorption. As shown in Fig. 3, C60–TPA–(Fc)2, showed weak fluo-
rescence at 710 nm in nonpolar toluene, whose fluorescence inten-

1820
J.H. Seok et al. / Journal of Organometallic Chemistry 694 (2009) 1818–1825
Fe
Fe
Br
CH3
N
c)
d)
a)
b)
O
H
O
H
N
N H
N
Br
N
N
4
5
6
C60−TPA−Fc (1)
Fe
Fe
Br
Br
Br
CH3
N
b)
c)
a)
d)
O
H
O
NH2
N
N
N
N
H
Br
Fe
Fe
7
8
9
C60−TPA−(Fc)2 (2)
Fe
Br
b)
e)
c)
d)
O
O
H
O
H
N
N
N
N
H
H
H
H
O
O
O
12
10
11
H3C
N
Fe
N
CH3
N
(C60)2−TPA−Fc (3)
Scheme 1. Synthesis of compounds 1, 2 and 3. (a) 1-Bromo-4-iodobenzene, Pd2dba3, dppf, NaOtBu, toluene, 100 °C, 15 h, 57.5% for 4, 48.5% for 7. (b) DMF, POCl3, 1,2-
dichloroethane, reflux, 24 h, 91.0% for 5, 42.7% for 8, 42.0% for 10. (c) vinyl ferrocene, K2CO3, Bu4NBr, Pd(OAc)2, DMF, 95 °C, 24 h, 65.0% for 6, 56.3% for 9, 40.0% for 12. (d) C60
N-methylglycine, toluene, reflux, 48 h, 15.3% for 1, 24 h, 17.7% for 2, 48 h, 50.0% for 3. (e) Br2, dichloromethane, r.t., 3 h, 87.0%.
,
sity was decreased very much compared with the reference C60
.
TPA–Fc in Fig. 4. The fluorescence time profile of the reference
The origin of the C60-fluorescence quenching is mainly attributed
to the Fc moiety attached to the TPA moiety, since such quenching
was not observed for C60-TPA in toluene [21].
C60 exhibited a single exponential decay with a lifetime (
sf) of
1.4 ns, which matches well with the reported value [41–43].
The fluorescence lifetimes (s
f) of the 1Cꢂ60 moiety of C60–TPA–Fc
In polar PhCN, almost all the fluorescence intensity of C60–TPA–
(Fc)2 was quenched. Since these observations are quite similar to
C60-TPA [21], the origin of the C60-fluorescence quenching is
mainly attributed to the attached TPA moiety to the C60 moiety.
The fluorescence time profiles observed by applying the 410 nm
could be evaluated from curve-fitting of the fluorescence time pro-
file with two exponential components, in which the main lifetimes
are shorter than 100 ps as summarized in Table 1, whereas the
minor long life times are about 1.3–1.4 ns. The sf values in polar
solvents are shorter than those in toluene, suggesting that attach-
ment of the TPA to the C60 moiety introduces a new quenching
pulsed laser light in the time range 0–1.2 ns are shown for C60
–

J.H. Seok et al. / Journal of Organometallic Chemistry 694 (2009) 1818–1825
1821
Fig. 2. Steady-state absorption spectra of C60–TPA–Fc; PhCN (benzonitrile), DCB (o-
dichlorobenzene), and TN (toluene).
Fig. 4. Fluorescence decay profiles of C60–TPA–Fc in toluene and DCB and C60 in
toluene as a reference; kex = 410 nm.
moiety accelerates the CS process between C60 and TPA as a den-
drimer effect [22]. On the other hand, bisfullerene tetrad (C60)2–
TPA–Fc shows almost the same kCS and UCS values compared to
those of monofullerene triad C60–TPA–Fc in the same solvents.
pathway for the 1C6ꢂ0 moiety. In addition, attachment of the Fc moi-
ety to TPA influences indirectly the C60-fluorescence quenching.
From the solvent dependence of the sf values, we infer a charge
separation (CS) quenching of the 1C6ꢂ0 moiety. The CS process from
ꢂ
1
the C60 moiety to the attached electron-donors can be supported
2.5. Nanosecond transient absorption spectra
by the negative
of the sf values was observed, which is a strong contrast to the sf
values of C60-TPA, showing f = 1.4 ns in toluene. Thus, the ob-
DGCS values. In toluene, appreciable shortening
The nanosecond transient absorption technique in the visible
and near-IR regions was performed to confirm the existence of
the CS state and to monitor the charge recombination (CR) pro-
cesses. The transient absorption spectra of (C60)2–TPA–Fc in DCB
are shown in Fig. 5, in which three spectra at different times after
the laser pulse are shown. Immediately after the laser pulse
(10 ns), a sharp peak with quick rise and decay component was ob-
served at 1000 nm, indicating the generation of the short lived
C60Åꢁ [44,45]. The immediate rise of the 1000-nm band after the la-
ser light pulse supports the very quick CS process, corresponding to
the fluorescence decay. From the decay of the 1000-nm band
shown in inset of Fig. 5, the CR rate constant (kCR) was evaluated
by the first-order curve-fitting to be 6.3 ꢃ 107 sꢁ1, which corre-
s
served short sf values for C60–TPA–Fc are induced by the attach-
ment of the Fc moiety to TPA, which implies that the Fc moiety
makes the CS process possible, generating C60Åꢁ–TPA–FcÅ+ even in
nonpolar toluene. Similar tendencies were observed for (C60)2–
TPA–Fc and C60–TPA–(Fc)2.
ꢂThe rate constants (kCS) and quantum yields (UCS) for CS via the
1C60 moieties were evaluated from the
sf values as listed in Table 1.
Both kCS and UCS values for C60–TPA–Fc, (C60)2–TPA–Fc and C60
–
TPA–(Fc)2 were found to be higher than those for C60-TPA in DCB
as well as in toluene, indicating that the additional effect of the
Fc group is present in less polar solvents. In highly polar solvents
such as PhCN, however, the kCS and UCS values are almost the same
as C60-TPA, indicating that extremely efficient CS takes place even
in C60-TPA without Fc moieties. Bisferrocene tetrad C60–TPA–(Fc)2
shows the larger kCS and higher UCS than those of monoferrocene
triad C60–TPA–Fc in all solvents used, suggesting that the extra Fc
sponds to the lifetime of the radical ion pair (
sRIP) such as
(C60 2
)
Åꢁ–TPA–FCÅ+ to be 16 ns in DCB. Since the broad absorption
Åꢁ
near 700 nm hides the absorption of the counter part of C60 in
the radical ion pair, the absorption due to the FcÅ+ moiety must
be burried.
In toluene, similar transient absorption spectra were observed.
The time profiles of the absorption peaks at 1000 and 700 nm con-
sist of two components. The fast decay component at 1000 nm of
Åꢁ
the C60 moiety gave the kCR of 2.1 ꢃ 107 sꢁ1 corresponding to a
lifetime for the radical ion pair (sRIP) of 48 ns in toluene. In PhCN,
only weak absorption peak with slow decay was observed at
ꢂ
3
700 nm due to the C60 moiety, but no extra peak due to the CS
state was observed, suggesting that the CR process is fast in highly
polar solvent. This trend is along the Marcus theory [46]; that is,
the CR process belongs to the inverted region of the Marcus parab-
ola due to larger
DGCR values than the small reorganization energy
[47–49]. The sRIP values for (C60)2–TPA–Fc in toluene and DCB are
longer than those of C60–TPA–Fc and C60–TPA–(Fc)2. Compared
with other monoferrocene-C60 radical ion pairs and multi-ferro-
cene-C60 radical ion pairs [50–52], the
TPA–Fc in toluene may be longest.
sRIP = 48 ns for (C60)2–
2.6. Energy diagram
The energy level diagram and photoinduced processes of
(C60)m–TPA–(Fc)n in DCB are shown in Fig. 6. After photoexcitation,
Fig. 3. Steady-state fluorescence spectra of C60–TPA–(Fc)2 in toluene (TN) and
benzonitrile (PhCN); kex = 410 nm.

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J.H. Seok et al. / Journal of Organometallic Chemistry 694 (2009) 1818–1825
Table 1
Short lifetimes (
ꢂ
1
s
f) and fractions, rates (kCS) and quantum-yields (UCS) of the charge-separation process via C60 and kCR of the radical ion pair.
a
b
b
Solvent
sf (ps)
kCS (sꢁ1
)
UCS
kCR (sꢁ1
)
C60–TPA–Fc
(C60)2–TPA–Fc
C60–TPA–(Fc)2
a
TN
DCB
PhCN
47 (70%)
33 (85%)
23 (68%)
2.1 ꢃ 1010
3.2 ꢃ 1010
4.5 ꢃ 1010
0.97
0.98
0.98
1.3 ꢃ 108
c
–
c
–
TN
DCB
PhCN
98 (67%)
49 (65%)
36 (57%)
9.5 ꢃ 109
2.0 ꢃ 1010
2.5 ꢃ 1010
0.93
0.97
0.97
2.1 ꢃ 107 (9.6 ꢃ 105)d
6.3 ꢃ 107
c
–
c
TN
DCB
PhCN
48 (67%)
25 (25%)
<10
2.0 ꢃ 1010
3.9 ꢃ 1010
>1 ꢃ 1011
0.97
0.98
>0.99
–
–
–
c
c
In parentheses, fraction of the short lifetime component.
b
kCS = (1/sf
)
sample ꢁ (1/sf
)
and UCS = [(1/sf
)
sample ꢁ (1/sf)ref]/(1/sf)sample. The minor long lifetimes were evaluated in the range of 1.0–1.3 ns. For C60-TPA, 1300 ps in
ref
toluene, 107 ps in DCB, and <50 ps in PhCN [21].
c
Too weak to detect or too fast.
This value may be affected by the triplet decay.
d
ꢂ
1
direct CS process takes pꢂlace via C60 to Fc over TPA (kC), as sup-
tral molecule, in addition to the triplet energy transfer to (C60)m–
3
*
posed by the observed 1C60-fluorescence quenching [53,54]. In less
TPA– (Fc)n, because of the lower triplet energy level of Fc
Å+
polar solvents, the energy level of (C60 m
)
Åꢁ–TPA–(Fc)n is between
[55,56]. In polar solvents, since the energy level of (C60 m
)
Åꢁ–TPA–
m–TPA–(Fc)n, the CR process to
1(C60
)
m–TPA–(Fc)n and 3(C60)m–TPA–(Fc)n; thus, the CR process
*
*
Å+
(Fc)n is lower than 3(C60
)
*
Åꢁ–TPA–(Fc)n to 3(C60
)
m–TPA–(Fc)n is possible with
*
Å+
*
3
from (C60 m
)
Fc (kCR) and to the ground state may be predominant.
kCR, as supported by the observation of huge transient absorption
at 700 nm (Fig. 5). Then, 3(C60)m–TPA–(Fc)n goes back to the neu-
*
3. Conclusion
Photoinduced electron transfer processes of two newly synthe-
sized tetrads with a TPA moiety as a central building block and ful-
lerene (C60) as an electron-acceptor and ferrocene (Fc) as an
electron-donor have been studied by the time-resolved spectro-
scopic techniques. In this paper, we succeeded in the syntheses
of bis-Fc tetrad C60–TPA–(Fc)2, and bisfullerene tetrad (C60)2–
TPA–Fc. Even in mono-Fc triad, efficient CS takes place via C60
better than the simple dyad C60-TPA. Compared with conventional
mono-Fc triad, new bisferrocene tetrad and new bisfullerene tetrad
showed efficient CS processes, supporting that the bisferrocene do-
nor effect, a kind of dendrimer effect, is working in the light har-
vesting photoinduced processes. It was found that the ratio of
electron-donor to C60 affects the CS efficiency via the excited sin-
0.10
0.015
4 ns
1000nm
50 ns
0.010
500 ns
0.08
0.005
0.06
0.04
0.02
0.00
0.000
1
*
0
50 100 150 200
Time/ ns
glet state of C60
.
600
700
800
900
1000
1100
4. Experimental
Wavelength/ nm
4.1. Materials and instruments
Fig. 5. Transient absorption spectra of (C60)2–TPA–Fc tetrad in Ar-saturated DCB;
kex = 532 nm. Inset: Time profile at 1000 nm.
Reagents and solvents were purchased as reagent grade and
used without further purification. All reactions were performed
using dry glassware under nitrogen atmosphere. Analytical TLC
was carried out on Merck 60 F254 silica gel plate and column chro-
matography was performed on Merck 60 silica gel (230–400
mesh). Melting points were determined on an Electrothemal IA
9000 series melting point apparatus and are uncorrected. NMR
spectra were recorded on a Varian Mercury-400 (400 MHz) spec-
trometer with TMS peak as reference. IR spectra were recorded
on a Nicolet 550 FT infrared spectrometer and measured as KBr
pellets. UV–Vis spectra were recorded on a Jasco V-550 spectrom-
eter. MALDI-TOF MS spectra were recorded with an Applied Bio-
systems Voyager-DE-STR. Elemental analyses were performed
with a Perkin–Elmer 2400 Analyzer.
kCS
1(C60)m*−TPA−(Fc)n
(C60)m.-−TPA−(Fc)n
.+
kCR
3(C60)m*−TPA−(Fc)n
h
kT
4.2. Synthesis
4.2.1. Synthesis of 1-bromo-4-diphenylaminobenzene (4)
To a solution of 1-bromo-4-iodobenzene (3.0 g, 10.0 mmol) in
toluene (50 ml) were added tris(dibenzylideneacetone)dipalla-
(C60)m−TPA−(Fc)n
Fig. 6. Energy diagram for (C60)m–TPA–(Fc)n in DCB.

J.H. Seok et al. / Journal of Organometallic Chemistry 694 (2009) 1818–1825
1823
dium(0) (Pd2dba3, 0.15 g, 0.16 mmol), 1,10-bis(diphenylphos-
69.23, 67.05, 40.45; IR (KBr):
m
= 2917, 2848, 2777, 1631, 1591,
phino)ferrocene (dppf, 0.12 g, 0.21 mmol) and stirred for 15 min.
Diphenylamine (1.79 g, 15.01 mmol), NaOtBu (1.15 g, 11.97 mmol)
were added to the reaction mixture and warmed to 100 °C and
then stirred for 15 h. After cooling, the solution was filtered and
the solvent was removed under reduced pressure. The product
was column chromatographed on silica gel with dichlorometh-
ane/hexane (1:10) to give compound 4 (2.79 g, 57.5%) in a white
solid. M.p. 113–115 °C; 1H NMR (400 MHz, CDCl3): d = 7.30 (d,
3H), 7.20 (d, 4H), 7.10 (d, 3H), 6.98 (t, 2H), 6.92 (d, 2H). Anal. Calc.
for C18H14NBr: C, 66.68; H, 4.35; N, 4.32. Found: C, 66.51; H, 4.66;
N, 4.10%.
1506, 1315, 1178, 811, 526 cmꢁ1; UV–Vis (toluene): kmax = 331,
431 nm; MS (MALDI-TOF): for C93H30N2Fe (M = 1231.09) m/z:
1233.10[M+2]+. Anal. Calc.: C, 90.73; H, 2.46; N, 2.28. Found: C,
90.70; H, 2.35; N, 2.25%.
4.2.5. Synthesis of N,N-bis(4-bromophenyl)aminobenzene (7)
To a solution of 1-bromo-4-iodobenzene (6.60 g, 23.60 mmol)
in toluene (100 ml) were added Pd2dba3 (0.09 g, 0.10 mmol), 1,10-
bis(diphenylphosphino)ferrocene (72 mg, 0.13 mmol) and stirred
for 15 min. Aniline (0.55 g, 5.91 mmol), NaOtBu (1.36 g,
14.10 mmol) were added to the reaction mixture and warmed to
100 °C and then stirred for 15 h. After cooling, the solution was fil-
tered and the solvent was removed under reduced pressure. The
product was column chromatographed on silica gel with dichloro-
methane/hexane (1:10) to give compound 7 (4.61 g, 48.5%) in a
colorless oil. 1H NMR (400 MHz, CDCl3): d = 7.31 (d, 3H), 7.24 (t,
3H), 7.04 (d, 3H), 6.91 (d, 4H). Anal. Calc. for C18H13NBr2: C,
53.63; H, 3.25; N, 3.47. Found: C, 53.60; H, 3.31; N, 3.44%.
4.2.2. Synthesis of 4-{N-(4-bromophenyl)-N-phenylamino}benzaldeh-
yde (5)
To a solution of compound 4 (1.0 g, 3.08 mmol) in 1,2-dichloro-
ethane (30 ml) were added DMF (0.81 ml, 10.80 mmol), POCl3
(1.80 ml, 10.80 mmol). The mixture was refluxed for 24 h and
cooled to r.t. The solution was poured into water (100 ml) and stir-
red for 30 min, and then the product was extracted with dichloro-
methane (3 ꢃ 100 ml). The organic layer was dried over MgSO4, the
solvent was evaporated. The residue was purified by column chro-
matography over silica gel with dichloromethane/hexane (3:1) to
give compound 5 (0.99 g, 91.0%) in a yellow solid. M.p. 103–
105 °C; 1H NMR (400 MHz, CDCl3): d = 9.78 (s, 1H), 7.66 (d, 2H),
7.40 (d, 2H), 7.31 (d, 2H), 7.13 (d, 2H), 7.00 (m, 5H). Anal. Calc.
for C19H14NOBr: C, 64.79; H, 4.01; N, 3.98. Found: C, 64.66; H,
4.12; N, 3.82%.
4.2.6. Synthesis of N,N-bis(4-bromophenyl)aminobenzaldehyde (8)
To a solution of compound 7 (0.35 g, 0.87 mmol) in 1,2-dichlo-
roethane (30 ml) were added DMF (0.20 ml, 2.61 mmol), POCl3
(0.24 ml, 2.61 mmol). The mixture was refluxed for 24 h and cooled
to r.t. The solution was poured into water (100 ml) and stirred for
30 min, and then the product was extracted with dichloromethane
(3 ꢃ 100 ml). The organic layer was dried over MgSO4, the solvent
was evaporated. The residue was purified by column chromatogra-
phy over silica gel with dichloromethane/hexane (3:1) to give com-
pound 8 (0.16 g, 42.7%) in a yellow solid. M.p. 158–161 °C; 1H NMR
(400 MHz, CDCl3): d = 9.91 (s, 1H), 7.69 (d, 2H), 7.30 (d, 4H), 6.98
4.2.3. Synthesis of 4-[N-{4-(2-ferrocenylvinyl)phenyl}-N-
phenylamino]benzaldehyde (6)
To a solution of compound 5 (0.71 g, 2.01 mmol) in DMF (50 ml)
were added vinyl ferrocene (0.51 g, 2.40 mmol), K2CO3 (3.47 g,
25.01 mmol), Bu4NBr (3.30 g, 0.01 mol), Pd(OAc)2 (50 mg,
0.25 mmol) and the mixture was warmed to 95 °C, and then stirred
for 24 h. The reaction solution was cooled to r.t. and filtered. The
solvent was removed under reduced pressure and the crude prod-
uct was washed with water and dried. The product was purified by
column chromatography over silica gel with dichloromethane/hex-
ane (2:1) to give compound 6 (0.63 g, 65.0%) in a orange color solid.
M.p. 79–82 °C; 1H NMR (400 MHz, CDCl3): d = 9.80 (s, 1H), 7.65 (d,
2H), 7.33 (m, 5H), 7.18 (d, 2H), 7.09 (d, 2H), 7.02 (d, 2H), 6.81 (d,
1H), 6.62 (d, 1H), 4.43 (s, 2H), 4.29 (s, 2H), 4.14 (s, 5H); IR (KBr):
(d, 6H); IR (KBr): m
= 2831, 2744, 1683, 1600, 1486 cmꢁ1. Anal. Calc.
for C19H13NOBr2: C, 52.93; H, 3.04; N, 3.25. Found: C, 52.85; H,
3.11; N, 3.12%.
4.2.7. Synthesis of N,N-bis{4-(2-ferrocenylvinyl)phenyl}aminobenzal-
dehyde (9)
To a solution of compound 8 (0.15 g, 0.35 mmol) in DMF (80 ml)
were added vinyl ferrocene (0.17 g, 0.81 mmol), K2CO3 (1.20 g,
8.68 mmol), Bu4NBr (1.11 g, 3.47 mol), Pd(OAc)2 (18 mg,
0.08 mmol) and the mixture was warmed to 95 °C, and then stirred
for 24 h. The reaction solution was cooled to r.t. and filtered. The
solvent was removed under reduced pressure and the crude prod-
uct was washed with water and dried. The product was purified by
column chromatography over silica gel with dichloromethane/hex-
ane (2:1) to give compound 9 (0.1 4 g, 56.3%) in a orange color so-
lid. M.p. 103–106 °C; 1H NMR (400 MHz, CDCl3): d = 9.91 (s, 1H),
7.68 (d, 2H), 7.38 (d, 4H), 7.20–7.03 (m, 6H), 6.82 (d, 2H), 6.64
(d, 2H), 4.45 (s, 4H), 4.29 (s, 4H), 4.14 (s, 10H); IR (KBr):
m
= 3411, 3083, 2805, 2728, 1689, 1585, 1506, 1330 cmꢁ1. Anal.
Calc. for C31H25NOFe: C, 77.03; H, 5.21; N, 2.90. Found: C, 76.90;
H, 5.41; N, 2.84%.
4.2.4. Synthesis of N-{4-(2-ferrocenylvinyl)phenyl}-N-[4-(1-methyl-
3,4-fullero-2,3,4,5-tetrahydropyrrol-2-yl)phenyl]-N-phenylamine (1)
Compound
6
(0.12 g, 0.23 mmol) and fullerene (0.20 g,
m
= 3089, 3033, 2915, 2724, 1689, 1589, 1506, 1324 cmꢁ1. Anal.
0.28 mmol), sarcosine (0.13 g, 1.40 mmol) were added to toluene
(120 ml) and refluxed for 48 h. The reaction mixture was cooled
to r.t., and the solvent was removed under reduced pressure. The
product was purified by column chromatography over silica gel
with toluene/hexane (2:1) to give compound 1 (43 mg, 15.3%) in
a black solid. M.p. >400 °C (dec.); 1H NMR (400 MHz, CDCl3):
d = 7.20–6.90 (m, 13H), 6.62 (d, 1H), 6.54 (d, 1H), 4.89 (d, 1H),
4.85 (d, 1H), 4.82 (s, 1H), 4.34 (s, 2H), 4.17 (s, 2H), 4.04 (s, 5H),
2.78 (s, 3H); 13C NMR (CDCl3): d = 156.43, 154.14, 153.79, 153.55,
147.68, 147.45, 146.99, 146.64, 146.52, 146.41, 146.34, 146.30,
146.24, 146.14, 146.08, 145.92, 145.67, 145.59, 145.47, 145.43,
145.39, 145.33, 145.28, 144.85, 144.78, 144.53, 143.31, 143.13,
142.81, 142.39, 142.29, 142.23, 142.19, 141.95, 141.80, 141.76,
140.31, 140.26, 140.05, 139.39, 137.99, 136.86, 136.70, 136.05,
135.93, 132.85, 131.45, 129.18, 128.38, 126.81, 125.73, 125.66,
125.46, 124.41, 83.98, 83.35, 77.78, 70.31, 69.95, 69.50, 69.27,
Calc. for C43H35NOFe2: C, 74.48; H, 5.09; N, 2.02. Found: C, 74.29;
H, 5.31; N, 1.94%.
4.2.8. Synthesis of N,N-bis{4-(2-ferrocenylvinyl)phenyl}-N-[4-(1-
methyl-3,4-fullero-2,3,4,5-tetrahydropyrrol-2-yl)phenyl]amine (2)
Compound
8 (0.09 g, 0.14 mmol) and fullerene (0.15 g,
0.20 mmol), sarcosine (0.07 g, 0.82 mmol) were added to toluene
(120 ml) and refluxed for 24 h. The reaction mixture was cooled
to r.t., and the solvent was removed under reduced pressure. The
product was purified by column chromatography over silica gel
with toluene/hexane (2:1) to give compound 2 (36 mg, 17.7%) in
a black solid. M.p. >400 °C (dec.); 1H NMR (400 MHz, CDCl3):
d = 7.36 (d, 2H), 7.32–7.11 (m, 6H), 6.99 (d, 4H), 6.72 (d, 2H),
6.60 (d, 2H), 5.01 (d, 1H), 4.92 (s, 1H), 4.90 (d, 1H), 4.43 (s, 4H),
4.29 (s, 4H), 4.16 (s, 10H), 2.89 (s, 3H); 13C NMR (CDCl3):
d = 156.43, 154.14, 153.79, 153.55, 147.68, 147.45, 146.99,

1824
J.H. Seok et al. / Journal of Organometallic Chemistry 694 (2009) 1818–1825
146.64, 146.52, 146.41, 146.34, 146.30, 146.24, 146.14, 146.08,
145.92, 145.67, 145.59, 145.47, 145.43, 145.39, 145.33, 145.28,
144.85, 144.78, 144.53, 143.31, 143.13, 142.81, 142.39, 142.29,
142.23, 142.19, 141.95, 141.80, 141.76, 140.31, 140.26, 140.05,
139.39, 137.99, 136.86, 136.70, 136.05, 135.93, 132.85, 131.45,
129.18, 128.38, 126.81, 125.73, 125.66, 125.46, 124.41, 83.98,
83.35, 77.78, 70.31, 69.96, 69.50, 69.28, 69.22, 67.03, 40.46; IR
black solid. M.p. >400 °C (dec.); 1H NMR (400 MHz, CDCl3):
d = 7.58 (br, 4H), 7.32 (d, 4H), 7.04 (d, 2H), 7.02 (d, 2H), 6.68 (d,
2H), 4.80 (d, 2H), 4.60 (s, 2H), 4.56 (d, 2H), 4.43 (s, 2H), 4.28 (s,
2H), 4.16 (s, 5H), 2.72 (s, 6H); 13C NMR (CDCl3): d = 148.58,
147.84, 147.49, 147.01, 146.27, 146.09, 145.75, 145.55, 145.12,
144.73, 144.41, 143.05, 142.59, 142.08, 141.58, 131.99, 131.27,
130.82, 129.85, 129.37, 128.75, 127.61, 126.94, 126.71, 126.25,
126.02, 124.95, 124.42, 124.17, 123.48, 121.40, 115.11, 83.98,
83.35, 69.83, 69.58, 69.15, 68.59, 68.11, 66.81, 66.45, 40.01,
(KBr):
m = 2944, 2915, 2775, 1631, 1596, 1504, 1178, 1105, 811,
526 cmꢁ1; UV–Vis (toluene): kmax = 366, 429 nm; MS (MALDI-
TOF): for C105H40N2Fe2 (M = 1441.14) m/z: 1439.80[M+1]+. Anal.
Calc.: C, 87.51; H, 2.80; N, 1.94. Found: C, 87.44; H, 2.92; N, 1.88%.
38.69; IR (KBr):
m
= 2944, 2921, 2775, 1737, 1693, 1590, 1504,
UV–Vis (toluene): kmax = 328,
1161, 1105, 818, 526 cmꢁ1
;
414 nm; MS (MALDI-TOF): for C156H35N3Fe (M = 2006.81) m/
z:1825.49 (MꢁFc)+. Anal. Calc.: C, 93.37; H, 1.76; N, 0.70. Found:
C, 93.31; H, 1.82; N, 0.68%.
4.2.9. Synthesis of N,N-bis(4-formylphenyl)aminobenzene (10)
To a solution of triphenylamine (10.0 g, 40.0 mmol) in DMF
(100 ml) was slowly added POCl3 (39.2 ml, 420.0 mmol) at 0 °C.
The mixture was warmed to 100 °C and stirred. After 6 h, the mix-
ture was cooled to r.t. and then carefully poured into saturated
aqueous Na2CO3 solution (300 ml). The mixture was stirred for
30 min, and then the product was extracted with ethyl acetate
(3 ꢃ 200 ml). The organic layer was dried over MgSO4, the solvent
was evaporated. The residue was purified by column chromatogra-
phy over silica gel with ethyl acetate/hexane (1:5) to give com-
pound 10 (5.06 g, 42.0%) in a yellow solid. M.p. 142–145 °C; 1H
NMR (400 MHz, CDCl3): d = 9.90 (s, 2H), 7.78 (d, 4H), 7.39 (m,
2H), 7.31–7.16 (m, 7H); Anal. Calc. for C20H15NO2: C, 79.72; H,
5.02; N, 4.65. Found: C, 79.80; H, 5.11; N, 4.42%.
4.3. Electrochemical measurements
Reduction potentials Ered and oxidation potentials Eox were
measured by cyclic voltammetry (CV) and Osteryoung square wave
voltammetry (OSWV) with a potentiostat BAS CV50W in a conven-
tional three-electrode cell equipped with Pt-working and counter-
electrodes with an Ag/AgNO3 reference electrode at scan rate of
100 mV/s. The Ered and Eox were expressed vs. Fc/Fc+ used as an
internal reference. In each case, a solution containing 0.2 mM of
a sample with 0.05 M of n-Bu4NClO4 (Fluka purest quality) was
deaerated with argon bubbling before measurements.
4.2.10. Synthesis of N-(4-bromophenyl)-N,N-bis(4-
4.4. Steady-state measurements
formylphenyl)amine (11)
To a solution of compound 10 (2.80 g, 9.30 mmol) in dichloro-
methane (100 ml) was slowly added bromine (1.70 g, 11.20 mmol)
and the mixture was stirred for 3 h. The solution was washed with
water (150 ml), aqueous Na2CO3 (2 ꢃ 100 ml) and the organic layer
was dried over MgSO4. The solvent was evaporated to gain com-
pound 11 (3.07 g, 87.0%) in a green solid. M.p. 217 °C; 1H NMR
(400 MHz, CDCl3): d = 9.90 (s, 2H), 7.80 (d, 4H), 7.51 (d, 2H), 7.18
Steady-state absorption spectra in the visible and near IR re-
gions were measured on a JASCO V570 DS spectrophotometer.
Steady-state fluorescence spectra were measured on a Shimadzu
RF-5300 PC spectrofluorophotometer equipped with photomulti-
plier tube having high sensitivity in the 700–800 nm region.
4.5. Time-resolved fluorescence measurements
(d, 4H), 7.06 (d, 2H); IR (KBr):
m = 2833, 2740, 1683, 1602,
1486 cmꢁ1. Anal. Calc. for C20H14NO2Br: C, 63.18; H, 3.71; N,
3.68. Found: C, 63.05; H, 3.88; N, 3.51%.
The time-resolved fluorescence spectra were measured by sin-
gle photon counting method using a streak-scope (Hamamatsu
Photonics, C4334-01) as a detector and the laser light second har-
monic generation SHG, 400 nm of a Ti:sapphire laser (Spectra-
Physics, Tsunami 3950-L2S, fwhm = 1.5 ps) as an excitation source.
Lifetimes were evaluated with software provided with the
equipment.
4.2.11. Synthesis of N-{4-(2-ferrocenylvinyl)phenyl}-N,N-bis(4-
formylphenyl)amine (12)
To a solution of compound 11 (3.0 g, 7.80 mmol) in DMF
(100 ml) were added vinyl ferrocene (2.0 g, 9.30 mmol), K2CO3
(3.50 g, 39.0 mmol), Bu4NBr (12.0 g, 39.0 mol), Pd(OAc)2 (0.2 g,
0.90 mmol) and the mixture was warmed to 95 °C, and then stirred
for 24 h. The reaction solution was cooled to r.t. and filtered. The
solvent was removed under reduced pressure and the crude prod-
uct was washed with water and dried. The product was purified by
column chromatography over silica gel with ethyl acetate/hexane
(1:9) to give compound 12 (1.6 g, 40.0%) in a orange color solid.
M.p. 133 °C; 1H NMR (400 MHz, CDCl3): d = 9.91 (s, 2H), 7.80 (d,
4H), 7.44 (d, 2H), 7.22 (d, 4H), 7.12 (d, 2H), 6.86 (d, 1H), 6.70 (d,
4.6. Nanosecond transient absorption measurements
Nanosecond transient absorption measurements were carried
out using the SHG (532 nm) of an Nd:YAG laser (Spectra Physics,
Quanta-Ray GCR-130, fwhm = 6 ns) as excitation source. For the
transient absorption spectra in the near IR region (600–
1600 nm), the monitoring light from a pulsed Xe-lamp was de-
tected with a Ge-avalanche photodiode (Hamamatsu Photonics,
B2834).
1H), 4.47 (s, 2H), 4.38 (s, 2H), 4.20 (s, 5H); IR (KBr):
m = 3088,
3031, 2915, 2724, 1689, 1589, 1508, 1324 cmꢁ1. Anal. Calc. for
C32H25NO2Fe: C, 75.17; H, 4.93; N, 2.74. Found: C, 75.09; H, 5.11;
N, 2.54%.
Acknowledgements
K.-Y. Kay acknowledges the financial support from Brain Korea
21 Program in 2006. M. El-Khouly thanks to JSPS program.
4.2.12. Synthesis of N-{4-(2-ferrocenylvinyl)phenyl}-N,N-bis[4-(1-
methyl-3,4-fullero-2,3,4,5-tetrahydropyrrol-2-yl)phenyl]amine (3)
Compound 12 (0.30 g, 0.58 mmol) and fullerene (1.0 g,
1.40 mmol), sarcosine (0.13 g, 6.90 mmol) were added to toluene
(30 ml) and refluxed for 48 h. The reaction mixture was cooled to
r.t., and the solvent was removed under reduced pressure. The
product was purified by column chromatography over silica gel
with dichloromethane to give compound 3 (0.58 g, 50.0%) in a
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